1. Field of the Invention
The present invention relates to an image processing apparatus capable of operating correspondence between a base image and a reference image, a method of controlling an image processing apparatus, and a computer-readable medium recording a program for controlling an image processing apparatus.
2. Description of the Related Art
Three-dimensional measurement of a moving image is highly demanded in the filed of face authentication, motion capture, facial expression analysis, utterance analysis, and the like. As such dynamic three-dimensional measurement should follow movement of an object, a passive method such as a stereo method is more suitable than an active method such as scanning with laser beams or the like.
A stereo correspondence search algorithm using phase-only correlation (POC) (an algorithm bringing identical points in images consisting of a base image and a reference image, each of which is a stereo image, into correspondence with each other) has attracted attention in terms of its robustness and high accuracy. More specifically, according to the phase-only correlation method, correlation between a window on the base image and a window on the reference image is determined only based on a phase component, with an amplitude component being ignored. Accordingly, the phase-only correlation is not affected by the difference in brightness of the image caused by variation in gain or offset adjustment of cameras on the left and right, and it is capable of stable measurement. In addition, with attention being paid only on the phase, position deviation can be measured with high accuracy.
Japanese Laid-Open Patent Publication No. 2006-010392 discloses a through hole measurement system applying the phase-only correlation method to a stereo camera.
Sei Nagashima et al., “Improving Performance for Subpixel Image Matching Based on Phase-Only Correlation,” The Society of Instrument and Control Engineers Tohoku Chapter, 218th Workshop, Oct. 9, 2004, material number 218-15, discloses aliasing based on weighting of spectrum and reduction in noise influence in a POC operation.
Accuracy in stereo correspondence depends on a texture of an object. Accordingly, accuracy is deteriorated by noise of the camera in a low-contrast region, and operation of correspondence between the base image and the reference image has not properly been performed.